The present invention generally relates to multiplexed color video signal recording and reproducing apparatuses, and more particularly to a recording and reproducing apparatus which records a multiplexed signal on a recording medium at the time of a recording. The multiplexed signal is obtained by time base compressing at least one of two kinds of color difference signals, time-division-multiplexing the time base compressed color difference signal with the other color difference signal, and multiplexing the time division multiplexed signal with a luminance signal which is not subjected to a time base compression. At the time of a reproduction, the time base compressed color difference signal within the multiplexed signal which is reproduced from the recording medium, is time base expanded to the original time base. A reproduced color video signal is formed from the color difference signal which is returned to the original time base, the other color difference signal, and the luminance signal.
Among the existing color video signal recording and reproducing apparatuses such as video tape recorders (VTRs), the more popular recording and reproducing apparatuses separate a luminance signal and a carrier chrominance signal from a standard system composite color video signal. The standard system is a system such as the NTSC system, the PAL system, and the SECAM system. The separated luminance signal is frequency-modulated, and the separated carrier chrominance signal is frequency-converted into a low frequency range. The frequency converted carrier chrominance signal is frequency-division-multiplexed with the frequency modulated luminance signal and recorded on a recording medium. At the time of the reproduction, a signal processing opposite to the signal processing carried out at the time of the recording, is carried out to obtain a reproduced composite color video signal which is in conformance with the original standard system. In other words, the more popular recording and reproducing apparatuses employ the so-called low-band-conversion recording and reproducing system.
Other various recording and reproducing systems have been proposed besides the low-band-conversion recording and reproducing system. For example, there was a proposed recording and reproducing apparatus which was designed to subject two kinds of color difference signals which are obtained by frequency-demodulating the carrier chrominance signal to a time base compression, and also subject the luminance signal to a time base compression. According to this proposed recording and reproducing apparatus, the time base compressed signals are time-division-multiplexed, and the time division multiplexed signal is frequency-modulated and recorded on the recording medium. At the time of the reproduction, a signal processing opposite to the signal processing carried out at the time of the recording, is carried out to obtain a reproduced composite color video signal which is in conformance with the original standard system. An example of such a recording and reproducing apparatus may be found in the U.S. Pat. Nos. 3,781,463 and 4,245,235, for example. This proposed recording and reproducing apparatus takes into account the difference in the bands of the luminance signal and the color difference signals, and takes measures so that the color difference signals having the narrower band can be transmitted within the horizontal blanking period. In other words, one of the color difference signals which is transmitted within one horizontal scanning period (1H), is subjected to a time base compression into approximately 20% of 1H. In addition, to utilize the band effectively, the luminance signal is subjected to a time base compression into approximately 80% of 1H so as to occupy a band which is in the same range as the band of the time base compressed color difference signal, and transmitted. Further, the two color difference signals are time-division-multiplexed, as a line-sequential signal in which the two color difference signals are alternately transmitted for every 1H, with the time base compressed luminance signal. This time division multiplexed signal is supplied to a frequency modulator, and an output signal of the frequency modulator is recorded on the recording medium. At the time of the reproduction, a signal processing opposite to the signal processing carried out at the time of the recording, is carried out to obtain a reproduced composite color video signal. The recording and reproducing system employed in this proposed recording and reproducing apparatus, will hereinafter be referred to as a timeplex system.
According to the timeplex system which transmits the time-division-multiplexed signal, there is no duration in which the luminance signal and the color difference signal are transmitted simultaneously. In the case of the NTSC system color video signal and the
system color video signal, a mutual interference and moire may occur between the luminance signal and the color difference signals, because the luminance signal and the carrier chrominance signal are band-share-multiplexed and transmitted. However, such a mutual interference and moire will not occur according to the timeplex system. In addition, even when the color video signal of any one of the NTSC system, the PAL system, and the SECAM system is recorded by an azimuth recording and reproducing system on tracks having the horizontal synchronizing signals recorded in non-alignment between mutually adjacent tracks and then reproduced, there is substantially no crosstalk from the adjacent tracks due to the azimuth loss effect, and it is possible to obtain a reproduced picture of a high picture quality. This is because the time division multiplexed signal is recorded on the adjacent tracks in the form of a frequency modulated signal which is obtained by frequency-modulating by the time division multiplexed signal a high-frequency carrier which has a large azimuth loss effect.
The time base compressed luminance signal and the time base compressed color difference signal employed in the timeplex system, both have an energy distribution in which the energy is large in the low frequency range and the energy is small in the high frequency range. In other words, the time base compressed luminance signal and the time base compressed color difference signal assume a signal format which is suited for the frequency modulation. Thus, it is possible to obtain a large modulation index, and the signal-to-noise (S/N) ratio can be greatly improved. Moreover, it is possible to substantially eliminate a deviation in the reproducing time base when expanding the time base.
However, according to the timeplex system, the luminance signal which has a relatively wide band compared to the color difference signals, is also time base compressed and transmitted, as in the case of the color difference signals. For this reason, it is necessary to provide a complex and expensive time base compressing circuit which uses a high sampling frequency, exclusively for the luminance signal. As a result, there are problems in that the circuit construction of the recording and reproducing apparatus as a whole is complex, and the manufacturing cost of the recording and reproducing apparatus is high.
In addition, in the conventional recording and reproducing apparatus employing the timeplex system, separates a reproduced horizontal synchronizing signal from the reproduced time division multiplexed color video signal, in a synchronizing signal separating circuit. The time position of a pulse which is obtained by differentiating the separated reproduced horizontal synchronizing signal, is used as a reference to separate a reproduced time base compressed luminance signal and a reproduced time base compressed line-sequential color difference signal from the reproduced time division multiplexed color video signal. The time position of the pulse is also used as a reference to determine the starting points of write-in and read-out operations with respect to a memory so as to perform the time base expansion. Hence, a circuit must be provided to process the horizontal synchronizing signal, and the processing of the horizontal synchronizing signal is relatively troublesome to perform.
Further, the timeplex system requires a processing in which the horizontal synchronizing signal is separated from the luminance signal and is inserted into a predetermined position in the time division multiplexed color video signal so as to transmit the separated horizontal synchronizing signal as the horizontal synchronizing signal of the time division multiplexed signal. Thus, the processing of the horizontal synchronizing signal is relatively troublesome to perform. When transmitting the I-signal and the Q-signal as the color difference signals, there is a problem in that the I-signal is band-limited to the same extent as the Q-signal because the time base compression rates of the I-signal and the Q-signal are the same.